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DiyFp.java
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// Copyright 2010 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// Ported to Java from Mozilla's version of V8-dtoa by Hannes Wallnoefer.
// The original revision was 67d1049b0bf9 from the mozilla-central tree.
package org.mozilla.javascript.v8dtoa;
// This "Do It Yourself Floating Point" class implements a floating-point number
// with a uint64 significand and an int exponent. Normalized DiyFp numbers will
// have the most significant bit of the significand set.
// Multiplication and Subtraction do not normalize their results.
// DiyFp are not designed to contain special doubles (NaN and Infinity).
class DiyFp {
private long f;
private int e;
static final int kSignificandSize = 64;
static final long kUint64MSB = 0x8000000000000000L;
DiyFp() {
this.f = 0;
this.e = 0;
}
DiyFp(long f, int e) {
this.f = f;
this.e = e;
}
private static boolean uint64_gte(long a, long b) {
// greater-or-equal for unsigned int64 in java-style...
return (a == b) || ((a > b) ^ (a < 0) ^ (b < 0));
}
// this = this - other.
// The exponents of both numbers must be the same and the significand of this
// must be bigger than the significand of other.
// The result will not be normalized.
void subtract(DiyFp other) {
assert (e == other.e);
assert uint64_gte(f, other.f);
f -= other.f;
}
// Returns a - b.
// The exponents of both numbers must be the same and this must be bigger
// than other. The result will not be normalized.
static DiyFp minus(DiyFp a, DiyFp b) {
DiyFp result = new DiyFp(a.f, a.e);
result.subtract(b);
return result;
}
// this = this * other.
void multiply(DiyFp other) {
// Simply "emulates" a 128 bit multiplication.
// However: the resulting number only contains 64 bits. The least
// significant 64 bits are only used for rounding the most significant 64
// bits.
final long kM32 = 0xFFFFFFFFL;
long a = f >>> 32;
long b = f & kM32;
long c = other.f >>> 32;
long d = other.f & kM32;
long ac = a * c;
long bc = b * c;
long ad = a * d;
long bd = b * d;
long tmp = (bd >>> 32) + (ad & kM32) + (bc & kM32);
// By adding 1U << 31 to tmp we round the final result.
// Halfway cases will be round up.
tmp += 1L << 31;
long result_f = ac + (ad >>> 32) + (bc >>> 32) + (tmp >>> 32);
e += other.e + 64;
f = result_f;
}
// returns a * b;
static DiyFp times(DiyFp a, DiyFp b) {
DiyFp result = new DiyFp(a.f, a.e);
result.multiply(b);
return result;
}
void normalize() {
assert(f != 0);
long f = this.f;
int e = this.e;
// This method is mainly called for normalizing boundaries. In general
// boundaries need to be shifted by 10 bits. We thus optimize for this case.
final long k10MSBits = 0xFFC00000L << 32;
while ((f & k10MSBits) == 0) {
f <<= 10;
e -= 10;
}
while ((f & kUint64MSB) == 0) {
f <<= 1;
e--;
}
this.f = f;
this.e = e;
}
static DiyFp normalize(DiyFp a) {
DiyFp result = new DiyFp(a.f, a.e);
result.normalize();
return result;
}
long f() { return f; }
int e() { return e; }
void setF(long new_value) { f = new_value; }
void setE(int new_value) { e = new_value; }
@Override
public String toString() {
return "[DiyFp f:" + f + ", e:" + e + "]";
}
}